1. Field of the Invention
The present invention relates to a liquid supplying apparatus and a liquid ejecting apparatus, more particularly to a pressure control technique in a liquid supplying apparatus which supplies liquid to an inkjet head or the like.
2. Description of the Related Art
In order to stably operate an inkjet head and to stably supply ink to the inkjet head, internal pressure of the inkjet head and pressure of an ink flow channel should be controlled to be constant. A pump arranged in the ink flow channel is used as a device that controls such pressure. Meanwhile, when a pump is used to control the internal pressure of the inkjet head or the pressure of the ink flow channel, a pressure fluctuation attributable to a pulsating flow of the pump or the like may occur. Such a pressure fluctuation not only obstructs stable ink supply but may also interfere with stable operations of the inkjet head.
On the other hand, techniques are known in which a damper is arranged in an ink flow channel to suppress a pressure fluctuation in the ink flow channel or a fluctuation in internal pressure of an inkjet head. For example, a technique is known in which a capacity of a sub tank connected to an ink flow channel is varied to have the sub tank function as a damper which suppresses a pressure fluctuation in the ink flow channel.
Japanese Patent Application Publication No. 2007-076016 discloses an ink supply container having a configuration in which a capacity regulating device suppresses expansion of a flexible member of an ink container when setting an internal pressure of the ink container to a positive pressure to perform cleaning and restoration of a nozzle of a recording head, the capacity regulating device does not suppress expansion of the flexible member of the ink container when setting the internal pressure of the ink container to a negative pressure to perform printing by the recording head, a capacity when the internal pressure of the ink container is set to a positive pressure is kept approximately equal to a capacity when the internal pressure of the ink container is set to a negative pressure suitable for printing, and when cleaning and restoration is performed according to a pressurizing recovery method, the internal pressure of the ink container is set to a negative pressure optimal for printing by merely discharging a small amount of ink from the ink container.
However, an apparatus which realizes high-speed printing, high-quality printing, and printing on large-size media consumes a large amount of ink and a significant pressure variation occurs in an ink supply channel during ejection by an inkjet head. A large-sized damper mechanism is required for suppressing such significant pressure variations. With the configuration disclosed in Japanese Patent Application Publication No. 2007-076016, a stroke of the capacity regulating device needs to be increased to secure buffering performance. At the same time, increasing the stroke of the capacity regulating device inevitably results in an increased size of the apparatus. In addition, with the configuration disclosed in Japanese Patent Application Publication No. 2007-076016, since a positional variation of the flexible member occurs over time due to operations associated with pressure fluctuations, pressure control characteristics also change.